"Flight tests of a F-51H airplane with two different vertical—tail assemblies were made to determine lateral and directional stability and control characteristics. The airplane had satisfactory directional stability in the landing, approach, and wave-off conditions with either tail. In the power— on clean and glide conditions, however 9 the airplane had weak directional stability with the original tail. The production tail, which had a 7—inch fin extension and a shorter span rudder, improved the directional stability in the power-on clean and glide conditions, but the stability was still weak in the power—on clean condition. Increased altitude in either case caused a slight decrease in the stability. The rudder-trim-force change with speed with either vertical—tail assembly was high. The general aileron control characteristics were satisfactory hut the aileron effectiveness failed to meet the Army handling-qualities requirements. "
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